Atlantic Bluefin Tuna in the Gulf of Maine, I: Estimation of Seasonal Abundance Accounting for Movement, School and School-Aggregation Behaviour

Abstract

Direct assessment of the abundance of highly migratory pelagic species, such as tuna, is rarely available and most indices are based on catch information. We estimate the seasonal abundance of North Atlantic bluefin tuna, Thunnus thynnus, in the Gulf of Maine (GOM) from a 3-year aerial survey conducted with commercial spotter pilots, while also utilizing findings from analyses of tracking and tagging data. We apply statistical correction and calibration to seasonal abundance estimates accounting for measured changes in horizontal and vertical movement behaviour, size, shape and aggregation of bluefin tuna schools. Our approach relies on ecological knowledge of bluefin tuna to extrapolate survey observations across areas not sampled by correcting survey abundance estimates based on range of movement search pattern and depth preference. We demonstrate how separate findings obtained through the analysis of data collected across different spatial and temporal scales can be integrated to correct and calibrate estimates of population abundance. We obtain fitted estimates of seasonal abundance of bluefin tuna in the GOM during 1994-1996 in the range of 45,000-51,000 individuals. If tuna behaviour is not accounted for, we estimate that the base or residual survey precision would be 4-7% determined from analysis of recent spotter survey data in the study region. We estimate the precision in estimating seasonal abundance accounting for tuna behaviour to lie within a range of 1,301-3,302%. Under hypothetical future improvements in survey design that achieve a precision of 20% in transect length and placement, we calculate net-precision to lie within a range of 82-93%. This calculation assumes reducible uncertainty in school size estimation and irreducible uncertainty in movement and school-aggregation behaviour. We infer that survey precision could be further reduced by 43-32% to attain 10-50% in which a 3-8 years adaptive survey design may reliably detect a seasonal abundance trend.

Fine-scale vertical and horizontal movements of juvenile yellowfin tuna (Thunnus albacares ) associated with a subsurface fish aggregating device (FAD) off southwestern Taiwan

“…Newlands et al. () documented that the aggregation of bluefin tuna extended to 40–50 km. Gutenkunst et al.…”

Ecological drivers of spatial variability among fish fauna of 21 tropical Australian estuaries

“…All gears that integrate over depths produce samples requiring corrections for different volumes sampled as the depth of water sampled changes. However, position in the water column and the vertical extent of schools differ among species (Arnold et al 1997) and times (Newlands et al 2006), making the validity of correcting for depth uncertain, particularly in the case of tropical estuaries where even average depth distributions are incompletely studied. Additionally, for fish that occur throughout the water column, correcting for the depth of water would be appropriate; however, for species that are only found in a narrow depth range (e.g.…”

Aerial surveys to monitor bluefin tuna abundance and track efficiency of management measures

“…Promising results have been obtained from aerial surveys on juvenile Southern bluefin tuna Thunnus maccoyii (age 2-4, 8-30 kg) in the Great Australian Bight that are now used to construct an index of abundance (Eveson et al 2012). In the case of ABFT, aerial surveys on mature individuals (~196 cm, >226 kg) have been conducted in the Gulf of Maine and along their migration pathways at the Great Bahama Banks, known as the -Tuna Alley‖ (Hoggard 1995, Lutcavage and Kraus 1997, Lutcavage and Newlands 1999, Newlands et al 2006. However, the majority of these operations were performed using commercial spotter pilots and lacked a rigorous statistical sampling design.…”